On the jam page it says " you need to have a legal right for it". And yeah, it is pretty common to note it 
We aren’t lawyers here, we are devs, but if it is stated on the site, where you buy/download an asset that you can use it for free, then there is no problem. Many of those licences allows also to suit the asset to your needs.
And as he wrote:
And on the page there, there is a strict description of rules, so imho feel free to use it and give a proper credit. Changing the format isn’t a change you’d be sued for, you’re not changing the content 
The creator wants recognition, so be sure you just do it.
EDIT:
Erm, wait, there is a note about ogg files on some songs on the site, so read them carefully